refactor: thread app_config through lead and subagent task path (#2666)

* refactor: thread app config through lead prompt

* fix: honor explicit app config across runtime paths

* style: format subagent executor tests

* fix: thread resolved app config and guard subagents-only fallback

Address two PR review findings:

1. _create_summarization_middleware passed the original (possibly None)
   app_config into create_chat_model, forcing the model factory back to
   ambient get_app_config() and risking config drift between the
   middleware's resolved view and the model's view. Pass the resolved
   AppConfig instance through end-to-end.

2. get_available_subagent_names accepted Any-typed config and forwarded
   it to is_host_bash_allowed, which reads ``.sandbox``. A
   SubagentsAppConfig (also accepted upstream as a sum-type input) has
   no ``.sandbox`` attribute and would be silently treated as "no
   sandbox configured", incorrectly disabling the bash subagent. Guard
   on hasattr and fall back to ambient lookup otherwise.

Adds regression tests for both paths.

* chore: simplify hasattr guard and tighten regression tests

- Collapse if/else into ternary in get_available_subagent_names; hasattr(None, ...) is False so the explicit None check was redundant.
- Drop comments that narrate the change rather than explain non-obvious WHY (test names already convey intent).
- Replace stringly-typed sentinel "no-arg" in regression test with direct args tuple comparison.

---------

Co-authored-by: greatmengqi <chenmengqi.0376@bytedance.com>

backend/tests/test_run_worker_rollback.py

@@ -1,8 +1,12 @@
+import asyncio
+from types import SimpleNamespace
 from unittest.mock import AsyncMock, call
 
 import pytest
 
-from deerflow.runtime.runs.worker import _agent_factory_supports_app_config, _build_runtime_context, _rollback_to_pre_run_checkpoint
+from deerflow.runtime.runs.manager import RunManager
+from deerflow.runtime.runs.schemas import RunStatus
+from deerflow.runtime.runs.worker import RunContext, _agent_factory_supports_app_config, _build_runtime_context, _install_runtime_context, _rollback_to_pre_run_checkpoint, run_agent
 
 
 class FakeCheckpointer:
@@ -12,6 +16,73 @@ class FakeCheckpointer:
         self.aput_writes = AsyncMock()
 
 
+def test_build_runtime_context_includes_app_config_when_present():
+    app_config = object()
+
+    context = _build_runtime_context("thread-1", "run-1", None, app_config)
+
+    assert context["thread_id"] == "thread-1"
+    assert context["run_id"] == "run-1"
+    assert context["app_config"] is app_config
+
+
+def test_install_runtime_context_preserves_existing_thread_id_and_threads_app_config():
+    app_config = object()
+    config = {"context": {"thread_id": "caller-thread"}}
+
+    _install_runtime_context(
+        config,
+        {
+            "thread_id": "record-thread",
+            "run_id": "run-1",
+            "app_config": app_config,
+        },
+    )
+
+    assert config["context"]["thread_id"] == "caller-thread"
+    assert config["context"]["run_id"] == "run-1"
+    assert config["context"]["app_config"] is app_config
+
+
+@pytest.mark.anyio
+async def test_run_agent_threads_explicit_app_config_into_config_only_factory():
+    run_manager = RunManager()
+    record = await run_manager.create("thread-1")
+    bridge = SimpleNamespace(
+        publish=AsyncMock(),
+        publish_end=AsyncMock(),
+        cleanup=AsyncMock(),
+    )
+    app_config = object()
+    captured: dict[str, object] = {}
+
+    class DummyAgent:
+        async def astream(self, graph_input, config=None, stream_mode=None, subgraphs=False):
+            captured["astream_context"] = config["context"]
+            yield {"messages": []}
+
+    def factory(*, config):
+        captured["factory_context"] = config["context"]
+        return DummyAgent()
+
+    await run_agent(
+        bridge,
+        run_manager,
+        record,
+        ctx=RunContext(checkpointer=None, app_config=app_config),
+        agent_factory=factory,
+        graph_input={},
+        config={},
+    )
+    await asyncio.sleep(0)
+
+    assert captured["factory_context"]["app_config"] is app_config
+    assert captured["astream_context"]["app_config"] is app_config
+    assert run_manager.get(record.run_id).status == RunStatus.success
+    bridge.publish_end.assert_awaited_once_with(record.run_id)
+    bridge.cleanup.assert_awaited_once_with(record.run_id, delay=60)
+
+
 @pytest.mark.anyio
 async def test_rollback_restores_snapshot_without_deleting_thread():
     checkpointer = FakeCheckpointer(put_result={"configurable": {"thread_id": "thread-1", "checkpoint_ns": "", "checkpoint_id": "restored-1"}})